1. Field of the Invention
The present invention relates to a vibrator in a vibration type driving apparatus and a manufacturing method thereof. More particularly, the present invention relates to a vibrator in a linear ultrasonic motor (vibration type driving apparatus) and a manufacturing method thereof.
2. Description of the Related Art
Conventionally, as a linear ultrasonic motor which linearly drives an object to be driven, a vibration type driving apparatus as disclosed in U.S. Pat. No. 7,109,639 has been proposed.
Here, a driving principle of the linear ultrasonic motor (vibration type driving apparatus) like this will be described with reference to the drawings.
As shown in FIG. 8A which is a perspective view illustrating an exterior appearance of the linear ultrasonic motor, a linear ultrasonic motor 510 is constituted by a vibrating device 501, a slider 506, and a pressurizing member (not illustrated) for pressurizing the vibrating device toward the slider.
The vibrating device 501 is constituted by an electromechanical energy conversion element 505 such as a piezoelectric element or the like, and a vibrator which is integrally bonded to one surface of the electromechanical energy conversion element 505. Here, the vibrator includes a base 502 which is formed rectangularly, and two projection portions 503 and 504 which are formed convexly on the upper surface of the base.
In the ultrasonic motor, if a voltage of a specific frequency (also, called an alternating electric field) is applied to the piezoelectric element, plural desired vibration modes are excited, and then the excited vibration modes are superimposed, thereby generating a vibration for driving.
The linear ultrasonic motor illustrated in FIG. 8A causes the vibrating device 501 to perform excitation of two bending vibration modes respectively illustrated in FIGS. 8B-1 and 8B-2. Both the two bending vibration modes are out-of-plane bending vibration modes of the plate-like vibrating device 501.
More specifically, one of the two out-of-plane bending vibration modes is a second-order bending vibration mode (MODE-A: feeding mode) in the longitudinal direction of the vibrating device 501, and the other of the two out-of-plane bending vibration modes is a first-order bending vibration mode (MODE-B: upthrust mode) in the width direction of the vibrating device 501.
The shape of the vibrating device 501 is designed so that the resonance frequencies of the two out-of-plane bending vibration modes coincide with each other or come close to each other.
Each of the projection portions 503 and 504 is disposed in the vicinity of a position which is a node of vibration in the vibration of the MODE-A (feeding mode). Then, each of apical surfaces 503-1 and 504-1 of the projection portions performs pendular motion using the node of the vibration as a fulcrum by means of the vibration of the MODE-A, whereby the apical surfaces perform reciprocation motion in the X direction (feeding direction).
Further, each of the projection portions 503 and 504 is disposed in the vicinity of a position which is an anti-node (or a loop) of vibration of the MODE-B (upthrust mode). Thus, the apical surfaces 503-1 and 504-1 of the projection portions perform reciprocation motion in the Z direction (upthrust direction, or normal-line direction) by means of the vibration of the MODE-B.
These two vibration modes (MODE-A and MODE-B) are simultaneously excited so that a vibration phase difference between these modes comes near ±π/2, and these modes are then superimposed, whereby elliptic motion in the X-Z plane arises at each of the apical surfaces 503-1 and 504-1.
Thus, the slider 506 which has been pressurized and brought into contact with the vibrating device can be driven in one direction by means of the relevant elliptic motion. At this time, the projection portions 503 and 504 of the vibrating device 501 and the slider 506 repetitively make contact and non-contact at the driving frequency (tens of kilohertz or more) of the vibrating device 501. For this reason, if one of these elements does not have an appropriate spring characteristic, a satisfactory contact state cannot be obtained.
On the other hand, as described above, each of the projection portions 503 and 504 has such a function of amplifying the vibration in the X direction.
To satisfy the above-described two functions, United States Patent Application Publication US2009/167111 proposes a vibration type actuator (linear ultrasonic motor) which achieves quiet driving. Namely, in this vibration type actuator, as illustrated in FIGS. 9A to 9C, springiness is given to each of the projection portions, and each of the projection portions is designed to have an appropriate shape.
More specifically, in this vibration type actuator, projection portions 609 and 610 each of which has springiness is formed as additional members, and bonded to a base 602, whereby a vibrating device 601 is formed.
However, in the vibration type actuator described in United States Patent Application Publication US2009/167111, there is a limit to speeding up of a motor, as described later. Here, as one measure of driving a motor at higher speed, there is a method of enlarging a vibration amplitude of the projection of the vibrating device in a feeding direction (X direction).
Further, as one of the methods of enlarging the vibration amplitude of the projection in the feeding direction (X direction), there is a method of increasing the height of the projection.
However, in the vibration type driving apparatus described in U.S. Pat. No. 7,109,639, although speeding up can be achieved if the height of the projection is increased, it is not avoided that costs increase in a manufacturing process.
In the vibration type actuator described in United States Patent Application Publication US2009/167111, if the height of the projection portion of the vibrating device is increased, the rigidity of the projection portion decreases in the feeding direction, whereby driving efficiency decreases. Moreover, it becomes difficult to set a vibration angle of the apex of the projection portion to a desired value in the feeding mode. As a result, unnecessary amplitude arises in the Z direction, whereby there is a fear that contact between the projection portion and the slider becomes unstable.
The present invention has been completed in consideration of such problems as described above, and an object of the present invention is to provide a vibrator in a vibration type driving apparatus in which the vibrator capable of achieving speeding up can be manufactured at low cost and a manufacturing method of the vibrator.